Table of Contents - The Atmospheric Studies Group at TRC

Section 1: Introduction
Application, Inc. (SAI) served as a subcontractor to Sigma Research with the responsibility for
developing the wind field modeling component of the system.
The original design specifications for CALPUFF included: (1) the capability to treat time-varying
sources, (2) suitability for modeling domains from tens of meters to hundreds of kilometers from a
source, (3) predictions for averaging times ranging from one-hour to one year, (4) applicability to inert
pollutants and those subject to linear removal and chemical conversion mechanisms, and, (5) applicability
for rough or complex terrain situations. The modeling system developed to meet these objectives
consisted of three components:
CALMET, a meteorological modeling package with both diagnostic and prognostic wind field
generators
CALPUFF, a Gaussian puff dispersion model with chemical removal, wet and dry deposition,
complex terrain algorithms, building downwash, plume fumigation, and other effects
CALPOST and other postprocessing programs for the output fields of meteorological data,
concentrations and deposition fluxes.
In July, 1987, CARB initiated a second project with Sigma Research to upgrade and modernize the Urban
Airshed Model (UAM) to include state-of-the-science improvements in many of the key technical
algorithms including the numerical advection and diffusion schemes, dry deposition, chemical
mechanisms, and chemical integration solver. The new photochemical model, called CALGRID
(Yamartino et al., 1992; Scire et al., 1989), was integrated into the CALMET/CALPUFF modeling
framework to create a complete modeling system for both reactive and non-reactive pollutants. A third
component of the modeling system, a Lagrangian particle model called the Kinematic Simulation Particle
(KSP) model (Strimaitis et al., 1995; Yamartino et al., 1996), was developed under sponsorship of the
German Umweldbundesamt. All three models (CALPUFF, CALGRID, and KSP) are designed to be
compatible with the common meteorological model, CALMET, and share preprocessing and
postprocessing programs for the display of the modeling results.
CALMET, CALPUFF, and CALPOST have been substantially revised and enhanced over time, and the
modeling system has achieved regulatory status. The U.S. EPA has designated the CALPUFF modeling
system as a Guideline ("Appendix A") model for regulatory applications involving long range transport,
and on a case-by-case basis for near-field applications where non-steady-state effects (situations where
factors such as spatial variability in the meteorological fields, calm winds, fumigation, recirculation or
stagnation, and terrain or coastal effects) may be important.
In the early 1990s, the Interagency Workgroup on Air Quality Modeling (IWAQM) reviewed various
modeling approaches suitable for estimating pollutant concentrations at Class I areas, including the
individual and cumulative impacts of proposed and existing sources on Air Quality Related Values
(AQRVs), Prevention of Significant Deterioration (PSD) increments, and National Ambient Air Quality
Standards (NAAQS). IWAQM consists of representatives from the U.S. Environmental Protection
Agency (EPA), U.S. Forest Service, National Park Service, and U.S. Fish and Wildlife Service. IWAQM
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